In electrophoresis an ionically-charged particle moves through a medium due to the influence of an applied electric field. The concept of electrophoresis can be combined with the principles of ‘Total Internal Reflectance’ (TIR) to create addressable displays. A suspension of particles can be used to controllably frustrate TIR and switch the state of pixels in such displays in a cotrolled manner. For example, an electromagnetic field can be applied to move charged particles in the suspension through an electrophoretic medium toward or away from an evanescent wave region to frustrate TIR at selected pixel portions of the region. In order for the electronic display to be useful the display should have quick response times. Further it is desirable that there is good contrast between the dispersed particles and the white background and that the electrophoretically active suspension remains stable.
It is known that repeated switching of a display which utilizes electrophoretically-mobile particles can result in a non-uniform distribution or movement of the particles, gradually causing the formation of particle clusters which deteriorates the quality of images produced by the display over time. An example is found in Dalisa, A., “Electrophoretic Display Technology,” IEEE Transactions on Electron Devices, Vol. 24, 827–834, 1977; and Mürau et al, “The understanding and elimination of some suspension instabilities in an electrophoretic display,” J. Appl. Phys., Vol. 49, No. 9, September 1978, pp. 4820–4829. It has been shown that such undesirable clustering can be reduced by encapsulating groups of suspended particles in separate micro-fluidic regions. See for example Nakamura et al, “Development of Electrophoretic Display Using Microencapsulated Suspension,” Society for Information Display Symposium Proceedings, 1014–1017, 1998 and Drzaic et al, “A Printed and Rollable Bistable Electronic Display,” Society for Information Display Symposium Proceedings, 1131–1134, 1998.
In summary it is desirable for an electronic display to have long term stability, quick response time and high contrast between the background and image being displayed. The invention has discovered that certain compositions have a combination of physical properties which overcome these obstacles in particular on electrophoresis.